I think it's just that the very largest codebases are the most likely to end up depending on obscure bugs in Ruby or the surrounding ecosystem itself, or maybe

I think it's just that the very largest codebases are the most likely to end up depending on obscure bugs in Ruby or the surrounding ecosystem itself, or maybe features that basically nothing ever uses except that one file buried deep in that one gem that three real programs use. Ruby apparently has a lot of stuff like that.